The primary objective is the understanding of dynamic processes in cholesterol gallstone formation and digestion involving bile salts. The effect of bile composition upon the nucleation and growth of gallstones will be studied using microscopy and the Coulter Counter. The physiochemical properties of mixed micelles that occur in bile in the gallbladder and in the gut during digestion will be determined by two techniques. Surfactant electrodes will be used to monitor the surfactant monomer concentration in micellar solution and the diffusion of mixed micelles will be determined using the Taylor Dispersion technique. The dissolution of fatty acids and monoglycerides by bile salts will be studied with a modified spinning disc.